A gas permeable membrane system may be used as a stand alone system to preferentially permeate one of the gas components from a multi component gas stream, e.q., hydrogen may be preferentially separated from a multiple component gas stream containing hydrogen. The less permeable gas components will consist of a gas mixture including hydrogen. The operation of the membrane system may be selectively adjusted so that the syngas stream is derived from the less permeable product stream, i.e., where the ratio of hydrogen to carbon monoxide in the non-permeate stream satisfies the desired syngas ratio. However, the gas membrane will pass a portion of less permeable gases along with the preferentially separated gas. To operate a gas membrane system which produces a low quality permeate reject stream of hydrogen and less permeable gases is clearly uneconomical.
Alternatively a proper syngas ratio between hydrogen and carbon monoxide from a multiple component gas stream containing hydrogen and carbon monoxide may also be produced from a PSA system by rejecting or recovering high purity hydrogen product and using the tail gas produced from the PSA unit in combination with a portion of the mixed gas feedstream to establish a mixed gas product having a desired syngas ratio of hydrogen and carbon monoxide. The tail gas effluent from the PSA system prior to such a combination, however, would have to be compressed such that its pressure is raised to the desired product pressure level. The compressor and PSA unit would have to be of a size and capacity large enough to accommodate a typical syngas feed supply which would make this alternative uneconomical as well.
A PSA unit has in the past been combined with a gas permeable membrane system to produce a high purity product essentially of a single gas component from a multi-component gas feed. In. U.S. Pat. No. 4,229,188, high purity hydrogen is recovered from a feed gas mixture containing hydrogen by passing the feed gas mixture to a selective adsorption unit to initially separate the hydrogen gas which is then further treated by a membrane system to recover additional quantity of hydrogen. Alternatively and as taught in U.S. Pat. Nos. 4,398,926 and 4,701,187, the feed gas mixture may initially be separated in a membrane separation unit to provide bulk separation of hydrogen. The separated hydrogen may then be passed to a PSA unit to achieve high purity hydrogen gas at high recovery. In U.S. Pat. No. 4,701,187, the tail gas purge stream from the PSA adsorption unit is also recycled back into the feed gas mixture to form an efficient system.
Accordingly, although the prior art teaches the combination of a membrane system with a PSA system to upgrade a low quality mixed gas stream in order to produce a high purity single component product, it is unknown to integrate a membrane system with a PSA system for producing a mixed gas product having an adjustably controlled gas ratio under varying and transient feedstream and operating conditions as well as a second high purity hydrogen product stream. It is also unknown to provide an integrated PSA and gas membrane system to produce a selected mixed gas product and a high purity single gas component product with essentially no loss of any of the gas components in the feedstream.